I. Technical Field
This invention pertains to the harvesting or recycling of energy, and particularly energy harvesting in apparatus which involve or comprise piezoelectric element(s).
II. Related Art and Other Considerations
A piezoelectric element is essentially a parallel plate capacitor with a dielectric material between the plates (the piezoceramic). As the piezoceramic material is strained, a charge builds up on the electrodes (plates). The strain on the piezoelectric material can result from various factors, such as vibration or even change of temperature (heating and cooling) of the piezoelectric material.
If the goal is to achieve the maximum energy transfer from a piezogenerator, then it is desirable to remove energy from the piezogenerator when the output voltage reaches a peak and the charge on the electrodes of the piezogenerator is maximized. This is because energy is voltage multiplied by charge, so that maximum energy transfer will be achieved when energy is extracted from the capacitor (of piezogenerator) when voltage of the piezogenerator is at a maximum and the charge on the capacitor of the piezogenerator is at its peak.
The problem of efficiently extracting energy from a piezogenerator has been explored. To date most significant advances in performance have been achieved using circuits such as that of FIG. 1 or circuits that require an external source to power the circuit. In FIG. 1, a piezoelectric device is connected between the terminals IN. Voltage across the piezoelectric device is rectified by a diode bridge rectifier circuit to result in a single polarity voltage which is applied to a charge storage device (which is represented as capacitance C1 in FIG. 1). The circuit of FIG. 1 also includes means such as switch Q1, to turn off the charge storage device C1 when the voltage applied to C1 is too small to be useful (since some devices might continue to draw power even though they cannot do anything and never turn off).